Within months, that annoyance can be fairly levelled at the O'Farrell government, which will start collecting more than half the fare on Sydney's privately owned airport line.

A revised 2005 contract between Airport Link Company, the owner of the stations on the airport line, and RailCorp gives the government 50 per cent of the revenue once the company reaches a certain level of income.

That threshold will be reached in March, giving RailCorp a boost of about $1.5 million a month.

About a year later, when Airport Link hits another threshold, the government share will jump to 85 per cent of its cash flow, or more than $2 million a month.

This presents the government with an opportunity to cut fares at the airport stations in line with the rest of the network. But the government says it has no plans to do so, with the Transport Minister, Gladys Berejiklian, confirming the money raised would go to general revenue. The domestic and international stations have a $12 ''station access fee'' on top of the RailCorp fare.

"Any revenue raised through the train service fee is already factored into the state government's forward estimates,'' she said.

Asked if she would consider lowering the station access fee to make airport trips cheaper, Ms Berejiklian said: "This is not current government policy."

Despite the higher fares for the two stations, train patronage to the airport has grown 40 per cent in the past three years.

About 5.7 million passengers are expected to use airport line stations this year, an increase of more than 1.7 million since 2009.

A decision last year to remove station access fees at the two non-airport stations on the line, Mascot and Green Square, has helped the patronage growth.

But the train trip is becoming increasingly popular with business travellers, in part because it can be less stressful than dealing with road traffic to the airport.

The line was finished in 2000 but high fares deterred passengers and receivers were appointed within six months. Its latest owner - a venture between Westpac and the Capital Partners fund - took over the line in 2007.